Fixed cryptic monotonic error

Author: korken89

CHANGELOG.md

@@ -14,6 +14,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Use swatinem rust-cache for GHA CI
+- Cryptic error message when writing `#[monotonic]`
 
 ## [v1.0.0] - 2021-12-25
 

src/parse.rs

@@ -9,10 +9,12 @@ mod util;
 
 use proc_macro2::TokenStream as TokenStream2;
 use syn::{
-    braced, parenthesized,
+    braced,
+    group::parse_parens,
+    parenthesized,
     parse::{self, Parse, ParseStream, Parser},
     token::Brace,
-    Ident, Item, LitBool, LitInt, Token,
+    Ident, Item, LitBool, LitInt, Path, Token,
 };
 
 use crate::{
@@ -368,14 +370,22 @@ fn task_args(
     .parse2(tokens)
 }
 
-fn monotonic_args(tokens: TokenStream2) -> parse::Result<MonotonicArgs> {
+fn monotonic_args(path: Path, tokens: TokenStream2) -> parse::Result<MonotonicArgs> {
     (|input: ParseStream<'_>| -> parse::Result<MonotonicArgs> {
         let mut binds = None;
         let mut priority = None;
         let mut default = None;
 
-        let content;
-        parenthesized!(content in input);
+        let content = match parse_parens(input) {
+            Ok(parens) => parens.content,
+            Err(_) => {
+                return Err(parse::Error::new(
+                    path.segments.first().unwrap().ident.span(),
+                    "expected opening ( in #[monotonic( ... )]",
+                ));
+            }
+        };
+
         if !content.is_empty() {
             loop {
                 // Parse identifier name
@@ -450,6 +460,7 @@ fn monotonic_args(tokens: TokenStream2) -> parse::Result<MonotonicArgs> {
                 let _: Token![,] = content.parse()?;
             }
         }
+
         let binds = if let Some(r) = binds {
             r
         } else {

src/parse/app.rs

@@ -457,7 +457,7 @@ impl App {
                         if monotonics.contains_key(&type_item.ident) {
                             return Err(parse::Error::new(
                                 span,
-                                "`#[monotonic]` on a specific type must appear at most once",
+                                "`#[monotonic(...)]` on a specific type must appear at most once",
                             ));
                         }
 
@@ -470,7 +470,8 @@ impl App {
 
                         check_monotonic(&*type_item.ty)?;
 
-                        let args = MonotonicArgs::parse(type_item.attrs.remove(pos).tokens)?;
+                        let m = type_item.attrs.remove(pos);
+                        let args = MonotonicArgs::parse(m)?;
 
                         check_binding(&args.binds)?;
 

src/parse/monotonic.rs

@@ -1,5 +1,5 @@
 use proc_macro2::Span;
-use proc_macro2::TokenStream as TokenStream2;
+use syn::Attribute;
 use syn::{parse, spanned::Spanned, ItemType, Visibility};
 
 use crate::parse::util::FilterAttrs;
@@ -9,8 +9,8 @@ use crate::{
 };
 
 impl MonotonicArgs {
-    pub(crate) fn parse(tokens: TokenStream2) -> parse::Result<Self> {
-        crate::parse::monotonic_args(tokens)
+    pub(crate) fn parse(attr: Attribute) -> parse::Result<Self> {
+        crate::parse::monotonic_args(attr.path, attr.tokens)
     }
 }
 

ui/monotonic-double.stderr

@@ -1,5 +1,5 @@
-error: `#[monotonic]` on a specific type must appear at most once
- --> $DIR/monotonic-double.rs:9:10
+error: `#[monotonic(...)]` on a specific type must appear at most once
+ --> ui/monotonic-double.rs:9:10
   |
 9 |     type Fast = hal::Tim1Monotonic;
   |          ^^^^

ui/monotonic-name-collision.stderr

@@ -1,5 +1,5 @@
-error: `#[monotonic]` on a specific type must appear at most once
- --> $DIR/monotonic-name-collision.rs:9:10
+error: `#[monotonic(...)]` on a specific type must appear at most once
+ --> ui/monotonic-name-collision.rs:9:10
   |
 9 |     type Fast1 = hal::Tim2Monotonic;
   |          ^^^^^

ui/monotonic-no-paran.rs

@@ -0,0 +1,8 @@
+#![no_main]
+
+#[mock::app]
+mod app {
+    #[monotonic]
+    type Fast = hal::Tim1Monotonic;
+}
+

ui/monotonic-no-paran.stderr

@@ -0,0 +1,5 @@
+error: expected opening ( in #[monotonic( ... )]
+ --> ui/monotonic-no-paran.rs:5:7
+  |
+5 |     #[monotonic]
+  |       ^^^^^^^^^